How to connect an HVAC Transducer to a Boron?

I am looking to control my HVAC Pressures with a Particle device, in particular the Boron. It boils down to a 2CP5 Transducer, needed to monitor the DC Voltage on one wire. That voltage has a corresponding pressure reading that can be converted in the software. Can I connect the transducer directly onto one of the pins? If so, is it an Analog or Digital Pin? Any code that I can reference? Any help would be really appreciated. LMK if you need any more information.

1 Like

@timshows ,

Welcome to the community!

I have used pressure transducers in some of my agriculture projects. If I have the part correct:

Then, this device sends an analog signal from 0.5-4.5V that is proportional to the pressure sensed. If this is correct, you could use one of the Boron’s analog inputs - but you must use a voltage divider.

The Boron is not 5V safe on its inputs so, you will need to build a voltage divider (340k / 660k for example) to ensure that the Boron does not see more than 3.3V. You can then back out this change in software along with your pressure / voltage calculations.

You will also need to supply this device with 5V perhaps using a boost converter.

Hope this helps,

Chip

1 Like

Since I’m guessing the OP wants to sample an existing transducer, I’ll add the need for protecting the existing control scheme/circuit from a failure of the Boron or it’s wiring.

In simple terms - you don’t want an external Boron/Wiring failure to drag down the HVAC Control’s Voltage measurement towards 0V, possibly causing the compressor to create an overpressure situation.

2 Likes

What you are explaining is exactly what I am trying to do. I did not know that a voltage divider needed to be in place. I also figured I would need something for the supply voltage but didn’t know what. I guess to make this a little less troublesome, I need to find or create a wiring schematic with these parts in place. It would also help to have the code to run and compile, but that is the least of my issues right now. Is this how you have your agriculture projects working? Thanks for your feedback, it has been invaluable so far.

@Rftop SO you are disagreeing with @chipmc on how he recommends setting this up? I am not sure what OP means, and I am not too sure I understand what you are suggesting… Is there something I am missing? Never the less, thanks for you any feedback that you can provide. it is much appreciated to me as a beginner.

1 Like

No Sir, I’m not disagreeing with Chip’s comments at all.

I “assumed” that you want to read the voltage from an existing pressure transducer that’s already installed in an existing system. If that’s not correct, then please disregard my post :wink:

1 Like

In addition to the voltage divider option, which is always a good choice when connecting a 5V sensor to a 3.3V ADC, there is one more option.

I have a 5V pressure sensor that theoretically can output too high of a voltage at full sensor pressure, however it would never be possible to achieve that pressure under normal circumstances. I ended up using a circuit like this. It allows the full resolution of the ADC, but prevents the device from being fried if the sensor fails and outputs the full 5V.

It also protects against voltage spikes on the line connected to the sensor. The chip is a D1213A TVS diode.

3 Likes

@rickkas7, that’s another great recommendation. I wish that I knew about that years ago.

If any guys/gals are interested, Anfield’s TI2C line of pressure transducers are 3V3, I2C output, and have low powered sleep modes (for battery operation).
They aren’t hobby-grade, but a great choice for a professional sensor when required by a project.

2 Likes

Looks real good. What is the price?

I am interested in all the information that I can receive. This thread has already been immensely helpful. But anything more is just icing on the cake.

This is the circuit/chip that would go between the transducer and the pin of the Boron Microcontroller, correct? Is there any other code that needs to be considered when programming the calculations? My transducer is for an HVAC, will that matter? Sorry for the annoying questions, I am relatively new at this…

@timshows, as mentioned by @rickkas7, you still need the voltage divider, which @chipmc mentioned earlier:

The calculation code approach will need to take into account the resistor ratio in the following:

Generally,
pressure = (full voltage range of ADC / full digital range of ADC) * ADC value read * resistor divider ratio,
  where ration = ratio of resistors, typically R1/R2 where R1 connects to the pressure sensor
  and R2 is connected to ground (the junction of the two is the PRES input of Ricks protection circuit)

pressure = (3.3 / 4095) * analogRead(ADC pin) * RATIO
1 Like

Does that Diode have 3 poles or just the 2? There are some with 6, 3 on each side of it…

The D1213 is a 3-terminal device.

Depending on the sensor, you may or may not need a voltage divider. For example, I have a 100 PSI sensor, which produces 3.3V at 75 PSI with a 5V supply. Since the maximum expected pressure is 65 PSI. I just use the D1213 diode to protect against overvoltage as I don’t need to measure pressures that high.

The line marked A3 in the center is what’s connected to the ADC pin on the Particle device.

The line marked PRES goes to the pressure sensor output.

The 100 ohm resistor prevents 3V3 from being directly connected to via a diode 5V in case the sensor wires get shorted.

2 Likes

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.